Topic: Reproduction
Aim: Describe the stages of embryonic development.
Directions: Read the paragraph below and answer questions 1-16
Following fertilization, the zygote moves through the oviduct propelled by involuntary smooth muscle contractions and
by the cilia lining the oviduct. Around 30 hours after fertilization, the zygote undergoes its first mitosis and cell division. This
process, called cleavage, continues, and by the third day, the embryo leaves the oviduct and enters the uterus. At this point, the
embryo is described as a morula—a solid ball of cells.
By the fifth day, the morula has developed into a blastula, which can be described as a hollow ball of cells. The blastula
attaches to the lining of the uterus (endometrium) around the sixth day and is fully implanted by Day 10. As time progresses,
one side of the blastula indents
to form a gastrula. The gastrula consists of three germ layers. The three layers, known as the endoderm, mesoderm and
ectoderm will start to develop into different cells and eventually different structures. This process is known as differentiation.
1. Identify the process that results in a zygote. ______________________________________
2. Draw the process of fertilization in the box labeled FERTILIZATION below. Be sure to identify the ZYGOTE.
3. Identify the name of the process in which the zygote undergoes mitotic cell division. ________________________________
4. Draw a 2-cell, 4-cell and 8-cell stage during cleavage in the box labeled CLEAVAGE below.
5. Identify the structure that forms as a result of cleavage. ______________________________________________________
6. Describe the structure of a morula. _________________________________________________________________________
7. Draw a morula in the box labeled MORULA below.
8. Identify the structure that forms AFTER the morula. ______________________________
9. Describe the structure of a blastula. ________________________________________________________________________
10. Draw a blastula in the box labeled BLASTULA below.
11. Identify the structure that the blastula attaches to in the female reproductive system. _________________________________
12. Identify the structure that forms after the blastula. ____________________________________________________________
13. Identify the three layers that make up the gastrula.
________________________________________________________________________________________________
14. Draw a gastrula in the box labeled GASTRULA below.
15. Identify and describe the process that occurs to the three germ layers that make up the gastrula.
____________________________________________________________________________________________________
___________________________________________________________________________________________________
16. Fill in DIFFERENTIATION into the appropriate location below.
FERTILIZATION
CLEAVAGE
MORULA
BLASTULA
GASTRULA